High strength al-cu-mg-ag-si alloy for cast product structural applications

ABSTRACT

The present invention relates generally to aluminum-copper-magnesium based alloys and products, and more particularly to aluminum-copper-magnesium-Silver-Silicon based alloys and products particularly suitable for aircraft structural applications and military vehicle structural applications requiring very high strength and ductility.

CROSS REFERENCES TO OTHER APPLICATIONS

This application claims priority from U.S. Provisional Application Ser. No. 61/573,782 filed on Sep. 12, 2011 and U.S. Provisional Application Ser. No. 61/626,790 filed on Oct. 3, 2011 bothl of which are incorporated by reference herein in their entirety. Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

This application is part of a government project. The research leading to this invention was supported by a Grant Number W911NF-07-2-0073 from the U.S. ARMY. The United States Government retains certain rights in this invention.

FIELD OF INVENTION

The present invention relates generally to aluminum-copper-magnesium based alloys and products, and more particularly to aluminum-copper-magnesium-silver-silicon based alloys and products particularly suitable as cast product for aircraft structural applications and military vehicle structural applications requiring very high strength and ductility.

BACKGROUND INFORMATION OF THE INVENTION Description of Related Art

Aluminum alloys containing copper, magnesium and silver are known in the art.

U.S. Pat. No. 4,772,342 describes a wrought aluminum-copper-magnesium-silver alloy including copper in the amount of 5.7 weight (wt.) percent (%), magnesium in an amount of 0.3-0.8 wt. %, silver in an amount of 0.2-1 wt. %, manganese in an amount of 0.3-1.0 wt. %, zirconium in an amount of 0.1-0.25 wt. %, vanadium in an amount of 0.05-0.15 wt. %, silicon less than 0.10 wt. %, and the balance aluminum.

U.S. Pat. No. 5,376,192 discloses a wrought aluminum alloy comprising about 2.5-5.5 wt. % copper, about 0.10-2.3 wt. % magnesium, about 0.1-1.0 wt. % silver, up to 0.05wt. % titanium and the balance aluminum, in which the amount of copper and magnesium together is maintained at less than the solid solubility limit for copper and magnesium in aluminum.

U.S. Pat. Nos. 5,630,889, 5,665,306, 5,800,927, and 5,879,475 disclose substantially vanadium-free aluminum-based alloys including about 4.85-5.3 wt. % copper, about 0.5-1 wt. % magnesium, about 0.4-0.8 wt. % manganese, about 0.2-0.8 wt. % silver, up to about 0.25 wt. % zirconium, up to about 0.1 wt. % silicon, and up to 0.1 wt. % iron, the balance aluminum, incidental elements and impurities. The alloy can be produced for use in extruded, rolled or forged products, and in a preferred embodiment, the alloy contains a Zr level of about 0.15 wt. %.

SUMMARY OF THE INVENTION

An object of the present invention was to provide a high strength, high ductility alloy, comprising copper, magnesium, silver, manganese, silicon and optionally dispersoid forming elements.

In accordance with the present invention, there is provided an aluminum-copper alloy comprising about 4.5-6.8 wt. % copper, 0.1-1.8 wt. % magnesium, 0.1-0.8 wt. % silver, 0.0-1.2 wt. % manganese, 0.25-1.2 wt. % silicon, the balance being aluminum and incidental elements and impurities such as, not limited to, iron up to 0.5%, zinc up to 0.5% and nickel up to 0.5 wt. %. Optionally one or more dispersoid forming elements selected from the group consisting of Titanium, Zirconium, Chromium, Scandium and Vanadium may be added in an amount up to 0.5 wt. % for titanium, 0.25 wt. % for zirconium, 0.5 wt. % for Cr, 0.5 wt. %, 0.8 wt. % for Sc, and 0.2 wt. % for V.

The inventive alloy can be manufactured and/or treated in any desired manner, such as by forming an extruded, rolled, or forged product. The present invention is further directed to methods for the manufacture and use of alloys as well as to products comprising alloys.

Additional objects, features, and advantages of the invention will be set forth in the description which follows, and in part, will be obvious from the description, or may he learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the several views and wherein:

FIG. 1. Photograph of the Constrained Rod Casting for alloyl 1238 showing no cracks;

FIG. 2. Photograph of the Constrained Rod Casting for alloy 11239 showing no cracks; and

FIG. 3. Photograph of the Constrained Rod Casting for alloy 11191 showing no cracks.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The high strength AL—CU—MG—AG—SI ALLOY for structural applications comprises a, high ductility alloy, comprising copper, magnesium, silver, manganese, silicon and optionally dispersoid forming elements.

One preferred embodiment of an aluminum-copper alloy comprises about 4.5-6.8 wt. % copper, 0.1-1.8 wt. % magnesium, 0.1-0.8 wt. % silver, 0.0-1.2 wt. % manganese, 0.25-1.2 wt. % silicon, the balance being aluminum and incidental elements and impurities such as, not limited to, iron up to 0.5%, zinc up to 0.5% and nickel up to 0.5 wt. %. Optionally one or more dispersoid forming elements selected from the group consisting of Titanium, Zirconium, Chromium, Scandium and Vanadium may be added in an amount of up to 0.5% for titanium, 0.25% for zirconium, 0.5 wt. % for Cr, 1.0 wt. %. 0.8 wt. % for Sc, and 0.2 wt. % for V.

The following examples describe preferred embodiments of the invention. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow the examples. In the examples all percentages are given on a weight basis unless otherwise indicated.

Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

These and other objects of the present invention will be more fully understood from the following description of the invention.

EXAMPLES Invented Alloys

The Laboratory scale ingots were cast with 2 inch thick by 5 inch wide by 15 inch long permanent mold for invented alloys (Alloy no. 11238, 11239 and 11191) and the baseline alloy, B206.

-   -   The alloy chemistries are shown in the TABLE 1:

TABLE 1 CHEMISTRY OF THE INVENTED ALLOYS and B206 (baseline alloy) (all chemistries are in wt. %) Alloy No Cu Mg Mn Ag Si Ti Zr Fe No. 11238 4.6 0.3 0.25 0.35 0.3 0.05 0.02 0.05 No. 11239 4.8 0.3 0.25 0.36 0.3 0.05 0.02 0.04 No. 11191 5.0 0.35 0.35 0.35 0.28 0.05 0.01 0.05 B206 (baseline) 4.6 0.25 0.4 — 0.10 0.01 — 0.06

Mechanical Properties

These ingots were homogenized at a temperature of 950 degree F. for 24 hours. These ingot were solution heat treated at 950 degree F. for 2 hours, followed by cold water quench. The water quenched product were age hardened for 4 hours at 350 deg F. in T6 temper condition The mechanical property test results from the peak strength aged material are shown in Table 2:

TABLE 2 TENSILE PROPERTIES OF THE INVENTED ALLOYS WITH THE BASELINE ALLOY B206. (0% cold work prior to age hardening process) Test 0.2% Yield Ultimate Elonga- ALLOY NO Direction Stress Tensile Strength tion No. 11238 Longitudinal 64.8 ksi 71.7 ksi 7.0% No. 11239 Longitudinal 66.2 ksi 70.7 ksi 4.3% No. 11191 Longitudinal 66.2 ksi 70.7 ksi 3.8% B206(Baseline) Longitudinal 51.3 ksi 59.6 ksi 5.1%

The comparison of the longitudinal direction tensile properties of the invented alloys, No 11238, No. 11239 and No. 11191 to the baseline alloy B206 in Table 2 demonstrated the high strength advantage of the inventive alloys with better or comparable ductility in −T6 temper condition.

Castability of the Invented Alloys

High strength alloys based on Al—Cu—Mg alloy system is known for their poor castability. However, the most surprising benefit of these invented alloys for cast product applications is their excellent castability showing high level of resistance against hot tearing during casting. To demonstrate the superior castability of these alloys, hot tearing tear resistance of these alloys were evaluated by utilizing “Constrained Rod Casting Mold” described in the excellent work published by Kamga et al. (“Hot Tearing of Aluminum-Copper B206 alloys with Iron and Silicon additions” Materials Science and Engineering. A527 (2010) pp 7413-7423). The photographs of the CRC Mold casting of these invented alloys are shown FIG. 1, FIG. 2 and FIG. 3 below demonstrating no cracks at all after casting by following the exact testing procedure described in the published work.

The foregoing detailed description is given primarily for clear understanding of the benefits of the new alloy compositions for cast product application, having optimum amount of alloying element of copper, magnesium, silver and silicone with dispersoid forming elements and incidental impurities. 

I claim:
 1. Aluminum based alloy cast product with alloy chemistries comprising from about 4.0-6.0 wt. % copper, from about 0.1-1.8 wt. % magnesium, from about 0.0-0.8 wt. % silver, from about 0.0-0.8 wt. % manganese, from about 0.1-1.2 silicon, and from about 0.0-0.12 titanium and the balance being aluminum and incidental elements and impurities.
 2. The alloy of claim 1, wherein said incidental element and impurities can includes iron.
 3. The alloy of claim 1, further comprising one or more dispersoid forming elements selected from the group consisting of chromium, zirconium, scandium and vanadium and combinations thereof.
 4. The alloy of claim 1, further comprising chromium in an amount of up to 0.8 wt. %, scandium in an amount up to 0.8 wt. %, and vanadium in an amount of up to 0.2 wt. % either in addition to, or instead of titanium.
 5. The alloy of claim 1 exhibit very high strength when the alloy is processed via solution heat treatment and age strengthening to T6 temper product for engineering structural applications having surprisingly high strength (i.e., no cold work or very low amount of cold work prior to final age strengthening step on the product of water quenched after solution heat treatment)
 6. The alloy of claim 1 is suitable for T8 temper application with even more pronounced high strength capability for engineering structural applications. 